Systems for reacting fuel and air to a reformate

ABSTRACT

The invention relates to a system for reacting fuel and air to a reformate. Said system comprises a reformer including a reaction chamber, a nozzle for supply a fuel/air mixture to the reaction chamber, at least one supply line for supplying fuel to the nozzle and at least one entrance channel for supplying air to the nozzle. According to the invention, the nozzle comprises a swirl chamber into which the at least one supply line for supplying fuel runs in a substantially axial/central manner and the at least one entrance channel runs in a substantially tangential manner and from which a nozzle outlet exits. The swirl chamber comprises a narrowing spiral channel into which the entrance channel for the gaseous medium runs, and a space axially contiguous thereto in the direction toward the nozzle outlet, into which the supply line for supplying fuel runs and from which the nozzle outlet exits.

CLAIM OF PRIORITY

This application claims the benefit of International Application PCT/EP02/02192, filed on Feb. 28, 2002, which claims benefit of German Application DE10117875.1, filed on Apr. 10, 2001, which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a system for reacting fuel and air to a reformate, comprising a reformer which has a reaction space, a nozzle for supplying a fuel/air mixture to the reaction space, at least one supply conduit for supplying fuel to the nozzle, and at least one entrance channel for supplying air to the nozzle.

BACKGROUND OF THE INVENTION

Generic systems are used for converting chemical energy into electric energy. For this purpose, fuel and air, preferably in the form of a fuel/air mixture, are supplied to the reformer. Inside the reformer, the fuel then is reacted with the atmospheric oxygen, preferably by performing the process of partial oxidation.

The reformate thus produced then is supplied to a fuel cell or a fuel cell stack, respectively, electric energy being released due to the controlled reaction of hydrogen, as part of the reformate, and oxygen.

As has already been mentioned, the reformer can be designed such that the process of partial oxidation is performed to produce reformate. In this case, when using diesel as fuel, it is particularly useful to perform preliminary reactions prior to the partial oxidation. In this way, long-chain diesel molecules can be converted to shorter-chain molecules with a “cold flame”, which ultimately promotes the operation of the reformer. In general, a gas mixture is supplied to the reaction zone of the reformer, which gas mixture is converted to H₂ and CO. Another constituent of the reformate is N₂ from the air and, in dependence on the air ratio and the temperature, possibly CO₂, H₂O and CH₄. In normal operation, the fuel mass flow is controlled corresponding to the required power, and the air mass flow is controlled to obtain an air ratio in the range of λ=0.4. The reforming reaction can be monitored by different sensors, for instance temperature sensors and gas sensors.

Beside the process of partial oxidation it is likewise possible to perform an autothermal reforming. In contrast to the autothermal reforming, the process of partial oxidation is effected in that a substoichiometric amount of oxygen is supplied. For example, the mixture has an air ratio of λ=0.4. The partial oxidation is exothermal, so that an undesired heating of the reformer can occur in a problematic way. Furthermore, the partial oxidation tends to lead to an increased formation of soot. To avoid the formation of soot, the air ratio λ can be chosen smaller. This is achieved in that part of the oxygen used for the oxidation is provided by steam. Since the oxidation with steam is endothermal, it is possible to adjust the proportion of fuel, oxygen and steam such that on the whole neither heat is released nor heat is consumed. The autothermal reforming thus achieved therefore eliminates the problems of the formation of soot and of an undesired overheating of the reformer.

It is likewise possible that subsequent to the oxidation inside the reformer further gas treatment steps are effected, and downstream of the partial oxidation there can in particular be provided a methanization.

A commonly used fuel cell system for instance is a PEM system (PEM=Proton Exchange Membrane), which can typically be operated at operating temperatures between room temperature and about 100° C. Due to the low operating temperatures, this type of fuel cell frequently is used for mobile applications, for instance in motor vehicles.

Furthermore, high-temperature fuel cells are known, so-called SOFC systems (SOFC=Solid Oxide Fuel Cell). These systems operate for instance in a temperature range of about 800° C., a solid electrolyte (solid oxide) being able to perform the transport of oxygen ions. The advantage of such high-temperature fuel cells as compared to PEM systems in particular consists in the ruggedness with respect to mechanical and chemical loads.

As field of application for fuel cells in conjunction with the generic systems not only stationary applications are considered, but also applications in the field of motor vehicles, for instance as auxiliary power unit (APU).

For a reliable operation of the reformer it is important to supply the fuel or the fuel/air mixture, respectively, to the reaction space of the reformer in a suitable way. For instance, a good mixing of fuel and air and a good distribution of the fuel/air mixture in the reaction space of the reformer are advantageous for the operation of the reformer. Within the scope of the present disclosure reference is always made to a fuel/air mixture when mentioning substances which have to be or have been introduced into the reaction space of the reformer. However, the substances introduced are not restricted to a mixture of fuel and air. Rather, other substances can also be introduced in addition, such as steam in the case of autothermal reforming. In so far, the term fuel/air mixture should be understood in this general form.

SUMMARY OF THE INVENTION

It is the object underlying the invention to provide a system for reacting fuel and air to a reformate, which has advantageous properties as regards the introduction of the fuel/air mixture into a reaction space of a reformer.

This object is solved with the features of the independent claims.

Advantageous embodiments and developments of the invention are indicated in the dependent claims.

The invention is based on the generic system in that the nozzle has a swirl chamber into which at least one supply conduit for supplying fuel opens substantially axially centrally and the at least one entrance channel opens substantially tangentially and from which exits a nozzle outlet, and that the swirl chamber comprises a narrowing spiral channel, into which opens the entrance channel for the gaseous medium, and a gap space axially contiguous thereto in the direction toward the nozzle outlet, into which opens the supply conduit for supplying fuel and from which exits the nozzle outlet. The arrangement of the invention thus provides that the entrance channel for the air or the gaseous medium in general opens into the annular space, while the supply for fuel, i.e. the liquid medium in general, opens into the gap space. The same in turn opens into the nozzle outlet and via its peripheral edge merges with the annular space or communicates with the same. Thus, the annular space performs the function of a turbulence chamber, into which the gaseous medium is introduced through a relatively large bore at least substantially tangentially at a relatively large distance from the central longitudinal axis of the swirl chamber. From the turbulence chamber or the spiral channel, respectively, the gaseous medium is introduced into a chamber with small axial extension. In the present case, this chamber is referred to as gap space. The small axial extension is chosen to be able to ensure a rather low pressure loss. An essential aspect of the system of the invention, in which there is provided a swirl chamber composed of a spiral channel and a gap space, relates to the maintenance of the spin with the objective to introduce the gaseous medium into the annular space at a low speed, to accelerate the same therein and introduce the same into the gap space at a high speed. At the axial outlet thereof, which in the present case is also referred to as nozzle outlet, a negative pressure thereby is provided such that the liquid medium axially flowing through the gap space is nebulized. The rheological design of the spiral channel can be effected according to the usual aspects of the design of deflectors for centrifugal fans, which are well known in the prior art.

The system in accordance with the invention in particular has an advantageous design in that one end wall of the spiral channel, i.e. the inner wall or the outer wall, is formed in a circular cylindrical shape, and the other end wall of the spiral channel is formed in a spiral shape. In this way, the spiral channel can be manufactured in two parts from a milled part provided with the spiral shape and a cylindrical part centrally inserted into the same.

Particularly preferably, the entrance channel for the liquid medium is arranged coaxially with respect to the nozzle outlet.

In particular, the liquid medium thus is centrally fed into the gap space in alignment with the central longitudinal axis of the swirl chamber through a small bore and on the side of the gap space directly opposite said bore is discharged through another larger bore; the same forms the nozzle outlet.

In this connection it is particularly preferable that the nozzle outlet is defined by a nozzle bore in an end plate of the gap space of the swirl chamber.

The edge of the nozzle outlet bore on the side of the gap space can be rounded, in order to minimize the pressure required to deliver the mixture of liquid and gaseous medium into the nozzle outlet. In another advantageous embodiment it is possible that this edge can be bevelled or can also be sharp-edged for the same purpose.

In a particularly advantageous way, the system in accordance with the invention is constituted such that the axial length of the nozzle outlet is 0.05 mm to 1 mm, in particular 0.1 mm to 0.5 mm.

Particularly preferably, means are provided so that secondary air can flow into the reaction space. In this connection, the air entering the reaction space through the nozzle, i.e. the air present in the fuel/air mixture, can be referred to as primary air. The secondary air advantageously is delivered through secondary air bores in the housing of the reaction space. Dividing the air into primary air and secondary air can be useful for providing a rich, readily ignitable mixture at the outlet of the nozzle. This is useful in particular during the starting operation of the system, as here the reformer advantageously operates in the manner of a burner.

Advantageously, the invention is developed in that the nozzle has means for holding a glow plug. The position of the glow plug with respect to the nozzle is an important parameter with regard to a good starting behavior of the reformer. In prior art devices, the glow plug generally was held by the reformer housing, so that this could lead to variations in position with respect to the nozzle. Due to the property of the inventive nozzle that the nozzle itself has means for holding the glow plug, such tolerances can be excluded. The glow plug always has the same position with respect to the nozzle.

In another preferred embodiment of the present invention it is provided that the means for holding the glow plug are realized as bore extending at an angle with respect to the nozzle axis. For the proper positioning, the glow plug then must merely be introduced into the bore. A stop at the glow plug and/or inside the bore ensures that the glow plug is guided into its optimum position with respect to the nozzle.

The invention is based on the knowledge that by means of a swirl chamber composed of a spiral channel and a gap space a particularly advantageous maintenance of the spin can be obtained. As a result, the gaseous medium, i.e. in particular the air, can be introduced into the annular space at a low speed, can be accelerated in the same, and from the same can then be introduced into the gap space at a high speed. In this way, a negative pressure is provided at the outlet of the gap space such that the liquid medium flowing through the gap space, i.e. in particular the fuel, is atomized or nebulized, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained by way of example by means of preferred embodiments with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic block circuit diagram of a system in which the present invention can be used;

FIG. 2 shows a partial longitudinal section of an embodiment of a nozzle for use in a system in accordance with the invention; and

FIG. 3 shows a cross-sectional view of the annular space of the swirl chamber of the nozzle as shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of the drawings, the same or comparable components are designated by the same reference numerals.

FIG. 1 shows a schematic block circuit diagram of a system in which the present invention can be used. Via a pump 240, fuel 216 is supplied to a reformer 214. Furthermore, air 218 is supplied to the reformer 214 via a blower 242. Via a valve means 222, the reformate 220 produced in the reformer 214 reaches the anode 224 of a fuel cell 212. Via a blower 226, cathode supply air 228 is supplied to the cathode 230 of the fuel cell 212. The fuel cell 212 produces electric energy 210. The anode waste gas 234 and the cathode waste air 236 are supplied to a burner 232. Reformate can likewise be supplied to the burner 232 via the valve means 222. In a heat exchanger 238, the thermal energy produced in the burner 232 can be supplied to the cathode waste air 228, so that the same is preheated. Waste gas 250 flows out of the heat exchanger 238.

The system illustrated in connection with the Figures described below can be used for supplying a fuel/air mixture to the reformer 214.

The low-pressure atomizer which in FIG. 2 is generally designated with the reference numeral 10 comprises a two-fluid nozzle 11 inserted in the wall 12 of a reformer. In detail, the two-fluid nozzle 11 includes a solid cylindrical base body 13, which from the rear side is inserted flush into a cylindrical blind-hole bore 27 of the wall 12. The relatively thin-walled wall portion 12A of the wall 12, which defines the blind-hole bore 27, is interrupted by a cylindrical aperture 28. On the right-hand side in FIG. 2, which corresponds to the exit of the two-fluid nozzle 11 into the reformer, the base body 13 has a recess 16 which defines the outer edge of a narrowing spiral channel 19.

Inside the spiral channel 19, coaxially with respect to the base body 13, a cylindrical recess 15 in the shape of a blind hole is provided, which has a larger axial extension than the spiral channel 19. Into the recess 15, a solid cylindrical part 17 is tightly inserted with a close fit, which protrudes from said recess axially extending into the spiral channel 19 and defines the inner contour thereof. The spiral channel 19 forms part of the swirl chamber of the two-fluid nozzle 11. An entrance channel 18 for a gaseous medium tangentially opens into the same. The entrance channel 18 continuously merges with the spiral channel 19 at the widest point thereof. With its narrowest point, the spiral channel 19 ends on the inside after about 360 degrees at the level of the entrance channel 18, separated from the same by a parting rib 20. At its front end (nozzle outlet end), the blind-hole bore 27 is closed almost completely by an end plate 21 and is merely interrupted by a central nozzle bore forming the nozzle outlet 23. The axial extension of the solid cylindrical part 17 is chosen such that between the front end face (the right-hand face in FIG. 2) of the cylindrical part 17 and the end plate 21 a gap space 22 is left, which due to the end face of the cylindrical part 17 has a circular shape and merges with the spiral channel 19 over its entire periphery. The spiral channel 19 and the gap space 22 together form the swirl chamber of the two-fluid nozzle 11.

The nozzle bore forming the nozzle outlet 23 is formed in alignment with the central longitudinal axis 14 in the end plate 21.

The two-fluid nozzle 11 also comprises a supply conduit 24 for a liquid medium, in particular fuel, which is traversed by a bore 25 of the solid cylindrical part 17 extending coaxially with respect to the central longitudinal axis 14 and which is received flush in an extension of the bore 25. The same is incorporated in the cylindrical part 17 proceeding from the rear side, and it extends along about half the axial length of the cylindrical part 17. Adjoining this bore in the cylindrical part 17 a bore 26 of smaller diameter is provided, which opens into the gap space 22. The axial extension of the gap space 22 is comparatively small with regard to a rather low pressure loss.

The base body 13 of the two-fluid nozzle 11 can additionally have a bore (not shown) extending at an angle with respect to the central longitudinal axis. For this purpose, either the base body 13 can have a diameter larger than shown or the spiral channel 19 can be arranged with less space required. Such bore (not shown) then can receive a glow plug (not shown), so that the position of the glow plug (not shown) with respect to the nozzle bore 23 then can be defined almost without any tolerance.

The operation of the low-pressure atomizer 10 is as follows. Via the entrance channel 18, gaseous medium, in particular air, is fed into the spiral channel 19 of the swirl chamber, and this air flows through this spiral channel into the gap space 22 of the swirl chamber under uniform pressure conditions. Via the bore 26, liquid medium, in particular fuel, is fed into the gap space 22, and this fuel is discharged from the opposed nozzle outlet 23 by the pressurized gaseous medium and thereby torn into fine droplets.

If it is desired, for instance, that fuel be introduced with a flow rate of 500 g/h, typical dimensions of the two-fluid nozzle 11 are as follows: The distance of the entrance channel 18 from the central longitudinal axis 14 is about 8 mm, and the free cross-section is about 4 mm. The axial extension of the gap space 22 is about 0.65 mm. The diameter of the nozzle bore forming the nozzle outlet 23 is about 2 mm, and its length is 0.05 mm to 1 mm (maximum length about 0.5 mm to 1 mm). With a two-fluid nozzle 11 of such dimensions, the minimum pressure required for atomizing the liquid medium is 30 mbar.

The features of the invention disclosed in the above description, in the drawings and in the claims can be essential for the realization of the invention both individually and in any combination.

List of Reference Numerals

-   10 low-pressure atomizer -   11 two-fluid nozzle -   12 wall -   12A wall portion -   13 base body -   14 central longitudinal axis -   15 recess -   16 recess -   17 cylindrical part -   18 entrance channel -   19 spiral channel -   20 parting rib -   21 end plate -   22 gap space -   23 nozzle bore -   24 supply conduit -   25 bore -   26 bore -   27 blind-hole bore -   28 aperture (in 12) -   64 glow plug -   210 electric power -   212 fuel cell -   214 reformer -   216 fuel -   218 air -   220 reformate -   222 valve means -   224 anode -   226 blower -   228 cathode supply air -   230 cathode -   232 burner -   234 anode waste gas -   236 cathode waste air -   238 heat exchanger -   240 pump -   242 blower -   250 waste gas 

1. A system for reacting fuel and air to a reformate, comprising a reformer which has a reaction space, a nozzle for supplying a fuel/air mixture to the reaction space, at least one supply conduit for supplying fuel to the nozzle, and at least one entrance channel for supplying air to the nozzle wherein, the nozzle comprises a swirl chamber into which the at least one supply conduit for supplying a liquid medium opens substantially axially centrally and the at least one entrance channel for supplying a gaseous medium opens substantially tangentially, and from which exits a nozzle outlet, and wherein the swirl chamber comprises a narrowing spiral channel, into which opens the entrance channel for the gaseous medium, and a gap space axially contiguous thereto in the direction toward the nozzle outlet, into which opens the supply conduit for supplying fuel, and from which exits the nozzle outlet.
 2. The system as claimed in claim 1, wherein one end wall of the spiral channel has a circular cylindrical shape and the other one has a spiral shape.
 3. The system as claimed in claim 1, wherein the entrance channel for the liquid medium is arranged coaxially with respect to the nozzle outlet.
 4. The system as claimed in claim 3, wherein the liquid medium is centrally fed into the gap space via a bore aligned with the central longitudinal axis of the swirl chamber and is discharged on the side of the gap space directly opposite said bore via another larger bore which forms the nozzle outlet.
 5. The system as claimed in claim 3, wherein the nozzle outlet is defined by a nozzle bore in an end plate of the gap space of the swirl chamber.
 6. The system as claimed in claim 4, wherein the edge of the nozzle outlet on the side of the gap space of the swirl chamber is rounded, bevelled or sharp-edged.
 7. The system as claimed in claim 4, wherein the axial length of the nozzle outlet is 0.050 mm to 1 mm.
 8. The system as claimed in claim 1, further comprising at least one secondary air bore.
 9. The system as claimed in claim 1, further comprising a glow plug.
 10. The system as claimed in claim 9, wherein the glow plug is held at an angle with respect to the nozzle axis.
 11. The system as claimed in claim 7, wherein the axial length of the nozzle outlet is 0.1 mm to 0.5 mm. 